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The evolution of adaptive immunity in vertebrates
Masayuki Hirano1, Sabyasachi Das, Peng Guo
1Emory Vaccine Center, Department of Pathology and Laboratory Medicine, Emory University, Atlanta, Georgia, USA.
Advances in Immunology
|May 17, 2011
Summary
Adaptive immune systems (AISs) in vertebrates evolved distinct recognition elements. Jawed vertebrates use V(D)J recombination and somatic hypermutation, while jawless vertebrates utilize variable lymphocyte receptors (VLRs) for pathogen defense.
Area of Science:
- Immunology
- Evolutionary Biology
- Vertebrate Zoology
Background:
- Two distinct recombinatorial adaptive immune systems (AISs) emerged in vertebrates ~500 million years ago.
- Jawed vertebrates rely on immunoglobulin-based receptors (T and B cells) generated via V(D)J recombination and somatic hypermutation.
- Jawless vertebrates possess an AIS based on variable lymphocyte receptors (VLRs) derived from diverse leucine-rich-repeat (LRR) sequences, lacking jawed vertebrate recognition elements.
Purpose of the Study:
- To investigate the evolutionary origins and diversification mechanisms of adaptive immune systems in jawed and jawless vertebrates.
- To compare the molecular underpinnings of receptor generation in these two distinct vertebrate lineages.
- To understand the selective pressures driving the evolution and maintenance of adaptive immunity.
Main Methods:
- Comparative analysis of immune system components and genetic mechanisms across jawed and jawless vertebrates.
- Examination of gene rearrangement processes, including V(D)J recombination and VLR generation.
- Review of molecular factors involved in adaptive immune receptor diversification, such as recombination-activating genes and activation-induced cytidine deaminase.
Main Results:
- Jawed vertebrate AIS relies on V(D)J gene segment rearrangement and somatic hypermutation; jawless vertebrates use VLRs from diverse LRR sequences.
- Transposon-like recombination-activating genes uniquely contributed to the AIS origin in jawed vertebrates.
- Activation-induced cytidine deaminase is utilized for receptor diversification in both jawed and jawless vertebrates.
Conclusions:
- The fundamental two-armed (T and B cell) AIS design evolved in a common ancestor of jawed and jawless vertebrates, predating their divergence.
- Distinct receptor construction strategies evolved, but the core AIS architecture has been conserved due to strong selection, likely for pathogen defense.
- The evolution of AIS highlights convergent and divergent strategies in immune receptor repertoire generation within vertebrates.
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